Answer:
The cost will be $3.50. See graph below.
TEACHER NOTES:
A piecewise function has different rules for different parts of its domain.[1]
[1] Bellmann, A., Bragg, S., Charles, R., Handlin, W., Kennedy, D.(2004); Prentice Hall Algebra 2, p. 71, Upper Saddle River, New York, Pearson Education, Inc.